R. Hay, R. Bembi, W. Sommerville
1982
Citations
0
Influential Citations
34
Citations
Journal
Inorganica Chimica Acta
Abstract
Abstract The syntheses of three new macrocyclic diamide ligands, 1,4,7,10-tetra-azacyclododecane-2,3-dione (L A ), 1,4,7,11-tetra-azacyclotridecane-2,3-dione (L B ) and 1,4,8,11-tetra-azacyclotetradecane-2,3-dione (L C ) are described. A number of copper(II) and nickel(II) complexes of these ligands have been characterised in the solid state. The complexes are non-electrolytes in aqueous solution due to ionisation of two amide protons to give neutral complexes [M(L2H)]. The yellow planar nickel(II) complex of L B , [Ni(L B 2H)] exists in equilibrium with the blue octahedral species [Ni(L B 2H)(H 2 O) 2 ]. For the octahedral ⇌ planar equilibrium, K = 0.51 at 25 °C, and the corresponding thermodynamic parameters are ΔH° = 4.23 kcal mol −1 and ΔS° 298 = +12.8 cal K −1 mol −1 . The copper(II) complexes of L A , L B and L C are oxidised in aqueous solution by hydrogen peroxide to give the corresponding copper(III) complexes. The copper(III) complexes are brownish-yellow in colour with d–d bands at ca. 350 nm. Cyclic voltammetry on the copper(II)/copper(III) and nickel(II)/nickel(III) redox systems with 1,4,8,11-tetraazacyclotetradecane-5,7-dione (L D ) indicate completely reversibility of the copper(II)/copper(III) couple in N,N-dimethylsulphoxide solution (E 1 2 = +0.43 V versus Ag/AgCl at 25 °C). The nickel(II)/nickel(III) couple is irreversible in aqueous solution.